Oxidation metod

ABSTRACT

The invention provides an oxidation method which utilizes a processing tube, a combustion chamber connected to the processing tube, inner and outer coaxial guide tubes connected to the combustion chamber, and an auxiliary combustion chamber connected to the combustion chamber, which includes the steps of placing a plurality of objects at predetermined intervals in the processing tube; generating steam in the combustion chamber by combustion of a mixture of oxygen and hydrogen gases and supplying the steam to the processing tube wherein the steam is generated by individually introducing oxygen gas and hydrogen gas into the combustion chamber through the outer and inner coaxial guide tubes and by heating the hydrogen gas in the inner guide tube or both the inner guide tube and the auxiliary combustion chamber such that ignition of the oxygen and hydrogen gases occurs when the gases come into contact with each other; and preventing a flame generated by the ignition of the gases from reaching an interior surface portion of at least one of the auxiliary combustion chamber and the combined chamber.

CROSS-REFERENCES TO THE RELATED APPLICATIONS

This application is a division of application Ser. No. 07/554,448, filedon Jul. 19, 1990, now abandoned, which is a continuation-in-part ofapplication Ser. No. 237,416, filed on Aug. 29, 1988 and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an oxidation apparatus for forming anoxide film on an object to be processed such as a semiconductor wafer(to be referred to as a wafer hereinafter).

2. Description of the Related Art

A conventional oxide furnace is of a horizontal type. In such ahorizontal furnace, a boat on which 150 wafers for example are mountedmust be loaded in/unloaded from a process tube by a cantilever fork.However, a deposit is adhered to the inner wall surface of the furnaceand the boat by the last annealing step. Therefore, if the fork flexesby its own weight, the deposit adhered to the boat is separated. As aresult, the deposit is adhered to the wafers as dust or an impurity.

In addition, the horizontal oxidation furnace requires a largeinstallation space. However, the cost per unit area in a clean room ishigh. Therefore, a strong demand has arisen for space saving of anoxidation furnace especially for wafers. However, the conventionalhorizontal oxidation furnaces cannot satisfy this requirement.

As for the above mentioned problems, it is difficult to automaticallycontrol the horizontal furnace or to increase its diameter. In addition,in the horizontal furnace, a temperature difference is produced betweenspaces above and below a wafer due to convection in the furnace,resulting in a poor yield. Furthermore, the intake of external O₂ islarge. As a result, in the horizontal furnace, an unnecessary oxide filmis formed and therefore the film thickness on a wafer is difficult tocontrol.

Conventionally, in order to form an oxide film on the surface of awafer, a wet oxidation method is adopted to obtain a steam atmosphere ina reaction tube.

As the wet oxidation method, a method called pyrogenic oxidation isgenerally utilized. In this method, as shown in FIG. 1, hydrogen gas 1and oxygen gas 2 are burned and combined in a combustion chamber togenerate steam. This steam is guided to a reaction tube 4 which houseswafers W, thereby obtaining a steam atmosphere in the tube 4.

Note that in FIG. 1, reference numeral 5 denotes a wafer boat; 6, a gasburner; 7, an oxygen supply path; 8, an oxygen and hydrogen flame; and9, a heater for heating hydrogen gas up to its ignition temperature.Then, high-temperature oxygen and hydrogen flame 8 comes closer to inletport upper wall portion 10 of combustion chamber 3 to cover portion 10.Since chamber 3 is formed of quartz, it is denatured when it is heatedto a high temperature. In the worst case, chamber 3 is melted andbroken. According to a conventional steam generation method, hydrogengas and oxygen gas is combusted and combined in the vicinity of the wallof a combustion chamber made of quartz, in order to prevent an accidentexplosion due to non-combustion of hydrogen gas.

As a result, the wall of the combustion chamber is heated and thetransparency of the wall is lost. In addition, molecules in the wall ofquartz, i.e. so called impurities, are dispersed in the combustionchamber and adhere to steam.

If such steam is employed in the oxidizing process or diffusing processof semiconductor devices, the resultant semiconductor devices have lowquality. Furthermore, since a tip portion of a hydrogen nozzle must bepositioned near a heat source, it is not possible to freely set thelocation at which hydrogen gas is combusted.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an oxidation apparatuscapable of preventing a combustion chamber from losing its transparency,and setting the location of the hydrogen gas.

Another object of the present invention is to provide an oxidationmethod which can form an oxide film on an object to be processed with ahigh yield, which can be automatically controlled, and a diameter ofwhich can be increased.

An oxidation apparatus is therefore provided, which comprises a processtube adapted to contain a boat in which a plurality of objects to beprocessed are placed at predetermined intervals; first heating means forheating an interior of said process tube; a combustion chamber, locatedoutside of and connected to said process tube via a connecting tube, forgenerating steam by combustion of a mixture of oxygen and hydrogen gasestherein and supplying the steam to said process tube; a double-tube typestructure connected to said combustion chamber, said double-tube typestructure having outer and inner guide tubes for individuallyintroducing the oxygen gas through said outer guide tube and thehydrogen gas through said inner guide tube into said combustion chamber;an auxiliary combustion chamber formed as an outlet portion of saidouter guide tube; an injection nozzle formed as an outlet portion ofsaid inner guide tube and located near a front end portion of saidauxiliary combustion chamber; and second heating means, provided aroundsaid outer guide tube, for heating the gases to a temperature at whichignition of the gases occurs when the gases come into contact with eachother wherein said auxiliary combustion chamber comprises an enlargementportion of said outer guide tube sufficient in size to prevent a flamegenerated by combustion of the gases from reaching a surface of saidauxiliary combustion chamber.

According to the present invention, an atmosphere forming means can beused. That is, the atmosphere forming means may be constituted by anexternal combustion unit for burning oxygen and hydrogen gases togenerate steam in a combustion chamber located outside the process tubeand supplying the steam to a gas inlet port of the process tube.

The external combustion unit can be used in the present invention, andit may be constituted by guide tubes for independently guiding oxygengas and hydrogen gas, a heating means, located around one or both of theguide tubes, for heating a gas in the guide tube to an ignition point ormore, a combustion chamber for bringing the oxygen and hydrogen gases,at least one of which is heated, into contact with each other andthereby burning and combining the gases into steam, and a supply tubefor supplying the steam to a gas inlet port of the process tube.

An auxiliary combustion chamber may be formed between the combustionchamber and the guide tube for hydrogen gas.

According to the oxidation method disclosed in the present invention,combustion gas (H₂) is not ignited and combusted by a heater. While H₂gas passes through a heater member, the H₂ gas is heated up to theignition point or above. The heated H₂ gas starts combustion in thepresence of oxygen. Specifically, the combustion gas supplied along withsteam at the flow rate of 15 l/min or above is first put in contact withoxygen at a predetermined location in the combustion chamber. In thecombustion chamber, the combustion gas has sufficient heat energy. Thus,the conditions for combustion are satisfied, and combustion of gas atthe optimal location in the combustion chamber is carried out.

According to the present oxidation method, when the hydrogen and oxygengases are supplied to the combustion chamber, the hydrogen gas of thegas burner starts combustion, steam is generated and at the same timeoxygen and hydrogen flames are generated. At this time, oxygen andhydrogen flames enter into the combustion chamber through the auxiliarycombustion chamber. However, this flame does not heat a portion close toan inlet port upper portion of the combustion chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic view for explaining a conventional combustionchamber adopting a pyrogenic oxidation method;

FIG. 2 is a schematic view for explaining a general arrangement of avertical apparatus;

FIG. 3 is a schematic view for explaining a state in which a hydrogengas guide tube is mounted;

FIG. 4 is a schematic view for explaining an arrangement of the hydrogengas guide tube;

FIG. 5A is a front view showing a combustion chamber, an oxygen guidetube, and a supply tube which are integrally formed;

FIG. 5B is a side view showing the combustion chamber, the oxygen guidetube, and the supply tube which are integrally formed;

FIG. 6 is an exploded perspective view showing an external combustionunit applied to the oxidation apparatus of the present invention;

FIG. 7 is a schematic view for explaining another embodiment of thepresent invention adopting an external combustion system;

FIG. 8 is a schematic view for explaining still another embodiment ofthe present invention not using an external combustion unit;

FIG. 9 is a schematic view for explaining still another embodiment ofthe present invention including an auxiliary combustion chamber;

FIG. 10A is an enlarged sectional view showing a gas burner;

FIG. 10B is an enlarged sectional view showing a gas burner of a stillanother embodiment; and

FIG. 11 is a schematic view for explaining an embodiment in which thegas burner and the combustion chamber are concentric.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment in which the present invention is applied to a verticaloxidation apparatus for a semiconductor wafer will be described belowwith reference to the accompanying drawings.

First, a general arrangement of the vertical oxidation apparatus used inthe present invention will be described below with reference to FIG. 2.This vertical oxidation apparatus has process tube 11 whose axialdirection is vertical. A heating unit, e.g., heater tube 13 is locatedaround process tube 11. Inlet port 12 for guiding steam is formed at anupper end of process tube 11. The heater tube 13 is for example a typeof resistance heating.

Quartz boat 14 is housed in process tube 11. Boat 14 supports aplurality of semiconductor wafers (not shown) so that the wafers arehorizontally supported and vertically spaced apart from each other. Boat14 can be vertically transported in process tube 11. Heat insulatingcylinder 15 is located at a lower end of boat 14. Cylinder 15 positionsboat 14 at a furnace core. Cylinder 15 is vertically moved by loaderunit 16. Boat 14 is loaded in/unloaded from process tube 14 by verticalmovement of cylinder 15. Note that the uniformity of a temperature and agas around semiconductor wafers in process tube 11 can be improved byrotatably arranging cylinder 15 so as to rotate the boat 14.

Handler 17 is located below process tube 11. Handler 17 grips andtransfers boat 14 to a boat transport unit.

In this apparatus, external combustion unit 10 is formed independentlyof process tube 11. In other words, the steam generator is locatedhorizontally above the process tube 11. That is, the steam generator isthe combustion unit 10 in this embodiment. Unit 10 burns oxygen andhydrogen gases and generates steam. This steam is supplied to gas inletport 12 at one end portion of process tube 11.

External combustion unit 10 has the following arrangement as shown inFIG. 3.

That is, unit 10 has guide tubes 20 and 30 for independently guidingoxygen gas and hydrogen gas. Preheating means 40 made of half heaters41, 42 is located around guide tubes 20 and 30. Half heaters 41, 42 heatgases in guide tubes 20 and 30 up to a temperature or more of anignition point. Half heaters 41, 42 and guide tubes 20 and 30 areconnected to combustion chamber 50. In chamber 50, the oxygen andhydrogen gases through the supply tube are burned and combined togenerate steam. The generated steam is supplied to inlet port 12 throughsupply tube 60.

Guide tubes 20 and 30 are formed as a coaxial double tube. That is,hydrogen gas guide tube 30 is arranged inside oxygen gas guide tube 20.

Note that guide tube 20 and chamber 50 are integrally formed. Guide tube20 and chamber 50 are formed of, e.g., quartz glass. Step structure 21ais formed between guide tube 20 and chamber 50 Guide tube 30 issupported by tube connector 34 as shown in FIG. 3. Nozzle 33 formed atthe distal end of guide tube 30 is located in chamber 50.

As shown in FIGS. 4 and 6, guide tube 30 is formed such that verticaltube 32 for guiding hydrogen gas is formed at one end of horizontal tube31 and nozzle 33 is formed at the other end thereof. Horizontal tube 31is, e.g. 8 mm in diameter. Nozzle 33 is inclined downward from thehorizontal direction of horizontal tube 31 by a predetermined angle θ.Nozzle 33 is, e.g., 4 mm in diameter smaller than guide tube 30. Angle θis set to be, e.g., five degrees. As a result, a flame generated byburning the oxygen gas, is not contacted directly with the wall ofcombustion chamber 50 formed of quartz glass.

Combustion chamber 50, oxygen gas guide tube 20, and supply tube 60which are integrally formed of quartz glass will be described below withreference to FIGS. 5A and 5B.

Guide tube 20 communicates with chamber 50 through large-diameter jointend 21a of horizontal tube 21. Vertical tube 22 branches from the otherend of horizontal tube 21. Oxygen gas is guided into chamber 50 throughvertical tube 22.

Chamber 50 has guide tube 20 at one end. Supply tube 60 is connected toa central portion on an outer surface of chamber 50. Steam supply tube60 comprises a large-diameter horizontal tube 61 and a small-diametervertical tube 62. The small-diameter is set, e.g., as 12 mm. One endportion of horizontal tube 61 communicates with chamber 50. Verticaltube 62 is formed at the other end portion of horizontal tube 61.

In this manner, steam supply tube 60 for oxidation is not formed at theend of chamber 50 opposite to the end connected to oxygen and hydrogenguide tubes 20 and 30. For this reason, the oxidation apparatus can bemade compact. In addition, unlike the case wherein supply tube 60 isformed at the end opposite to guide tube 30, a flame can be preventedfrom directly entering into supply tube 60. In addition, the thermalinfluence of chamber 50 to the outside can be reduced.

In order to connect supply tube 60 with inlet port 12, a Teflon(tradename) tube 63 is horizontally located as shown in FIG. 2. Heatingportion 66 such as a tape heater for preventing moisture condensation isformed around Teflon tube 63.

In order to connect Teflon tube 63, supply tube 60 and inlet port 12,quartz insert tube 66a is inserted into both ends of Teflon tube 63.These ends are connected with Teflon fittings 64.

Preheating means 40 located around guide tubes 20 and 30 constituting adouble tube will be described below referring to FIG. 6. Preheatingmeans 40 is formed by locating half heaters 41 and 42 above and belowthe double tube in a direction perpendicular to the diameter. Heaters 41and 42 are supported by box members 43 and 44, respectively. As shown inFIG. 6, box members 43 and 44 are supported so as to be freelyopened/closed through a hinge. This structure has the advantage of easymaintenance.

In order to detect temperatures of heaters 41 and 42, an R-typethermocouple 45 is utilized. Thermocouple 45 detects the temperatures sothat heating temperatures of heaters 41 and 42 are always maintained atabout, e.g., 850° C.

A support member for supporting chamber 50 is formed adjacent to heatingmeans 40. The support member is divided into lower support member 55 andupper support member 56. Inner surfaces of support members 55 and 56 areused as cooling portions for preventing heat dissipation from chamber50. That is, cooling water inlet ports 55a and 56a and cooling wateroutlet ports 55b and 56b for circulating cooling water are formed in theinner surfaces of support members 55 and 56, respectively. As theresult, the steam generated is cooled at a proper temperature fortransporting by the process tube 11. Outlet port 55b of support member55 is connected to inlet port 56a through SUS flexible tube 58. Notchportions 55c and 56c are formed in side surfaces of support members 55and 56, respectively. A flame detector 57 for detecting a flame inchamber 50 is located through notch portions 55c and 56c. When detector57 detects an abnormal flame, an alarm signal is fed back to a systemcontroller.

The oxidation method will now be described along with the operation ofthe apparatus.

First, quartz boat 14 is loaded in process tube 11. That is, loader unit16 supports heat-insulating cylinder 15. The central axis of the loaderunit 16 coincides with that of the process tube 11. Boat 14 isvertically placed on cylinder 15. In this state, each axis of the wafersloaded on the boat 14 is positioned nearly along the axis of processtube 11. Unit 16 is moved upward to transport boat 14 into process tube11. Note that since boat 14 is vertically supported, the semiconductorwafers are horizontally located in process tube 11.

In this case, the loading direction of boat 14 coincides with itsgravitational direction. For this reason, unlike in a conventionalhorizontal oxidation furnace, boat 14 is not brought into contact withthe inner surface of process tube 11 due to curvature, hanging, or thelike of a fork. Therefore, the generation of an impurity can beprevented so as to largely improve the yield of annealing performed onthe semiconductor wafers.

A steam atmosphere can be formed in process tube by external combustionunit 10. As for unit 10, a unit of a heat carrying system (JapanesePatent Application No. 62-43751) filed by the present applicant isadopted.

That is, in unit 10, oxygen gas is supplied to oxygen gas guide tube 20and hydrogen gas is supplied to hydrogen gas guide tube 30 at the flowrate of not more than 15 l/min. Note that the ratio between hydrogen andoxygen gases required for combustion for generating steam ispredetermined. However, if a large amount of oxygen gas is supplied, theoxygen gas not used for combustion can be used as a steam carrier to besupplied to process tube 11. It is a matter of course that the oxygengas is used to form an oxide film.

The oxygen and hydrogen gases are heated to a temperature, e.g., theignition point or more of the hydrogen gas before they are supplied tochamber 50. The energy required for combustion is given to the oxygenand hydrogen gases by this heating.

The hydrogen gas discharged from nozzle 33 to chamber 50 isinstantaneously brought into contact with the oxygen gas and ignites,thereby starting combustion. That is, it is characterized by the factthat preheating for a combustion temperature has been done before mixingthe oxygen gas and the hydrogen gas.

According to an experiment, when a temperature of heating means 40 wasabout 750° C., the hydrogen gas ignited even when the temperature nearnozzle 33 was lower than the ignition point of the hydrogen gas, e.g.,382° C. However, when the temperature of the heating means 40 was about730° C., the hydrogen gas did not ignite.

That is, even when the temperature at the combustion position is lowerthan an ignition point of hydrogen gas, the hydrogen gas ignites if itis heated up to its ignition point through guide tube 30. Hydrogen gasis heated at, e.g., 850° C. in this embodiment.

Note that neither oxygen gas nor air are present in guide tube 20.Therefore, ignition of the hydrogen gas in guide tube 20 can beprevented.

In this manner, hydrogen and oxygen gases are burned to generate steam.The temperature of the generated steam is more than 2000° C. It isdifficult to convey this high temperature steam. Thus, the steam iscooled about 200° C. After that, the steam is supplied into process tube11 through supply tube 60 and contributes to oxidation of semiconductorwafers (not shown). To get a low temperature steam, supply tube 62 whichsupplies the steam from chamber 50 to process tube 11, is formed throughthe wall of the chamber 50. If supply tube 62 is set on the axis of thechamber 50, it is necessary to set the cooling system beside the lowersupport member 55.

In this case, a flame is generated by combustion in chamber 50. However,since nozzle 33 of guide tube 30 is inclined downward from a horizontaldirection, a flame which tends to face upward is not brought into directcontact, or is brought into weak contact with an upper surface ofchamber 50. Therefore, a devitrification phenomenon in which chamber 50formed of quartz is obscured can be prevented. In addition, the quartzis not adhered to steam as an impurity. As a result, such an impurity isnot supplied into process tube 11, thereby improving the yield ofannealing performed to the semiconductor wafers.

Note that in this embodiment, steam is obtained by burning hydrogen andoxygen gases in external combustion unit 10. For this reason, an adverseinfluence of heat on process tube 11 during combustion can be prevented.In addition, the uniformity of temperature in process tube 11 can beeasily controlled by heater 13. In this the steam is supplied to processtube 11 through Teflon tube 63. Process tube 11 can be located at aposition separated away from unit 10. Therefore, an adverse influence onthe process tube can be further reduced. For this reason, the uniformityof a temperature at the oxide film formation region in process tube 11can be easily controlled. In addition, the uniformity of a flow of a wetgas can be assured. As a result, a uniform thickness of the oxide filmcan be obtained to improve the yield of annealing performed to thesemiconductor wafers.

Note that tape heater 66 is used to prevent moisture condensation ofsteam when the steam is supplied and cooled through Teflon tube 63.

As shown in FIG. 2, since external combustion unit 10 and gas inlet port12 are connected through horizontally located Teflon tube 63, the spaceabove process tube 11 can be reduced. As a result, the height of theoxidation apparatus can be reduced so that the apparatus can be used ina clean room the ceiling height of which is limited.

External combustion unit 10 used in this embodiment has the followingadvantages which an external combustion unit used in a conventionalhorizontal oxidation apparatus disclosed in Japanese Patent Disclosure(Kokai) No. 55-90405 does not have.

That is, in the conventional horizontal oxidation apparatus, a longhydrogen gas guide tube is inserted in a combustion chamber. Therefore,in order to prevent an explosion caused by incomplete combustion ofhydrogen gas, hydrogen and oxygen gases are burned and combined near thewall surface of the chamber.

For this reason, a portion near the wall surface is heated so as tocause devitrification, i.e., transparency is lost. In addition,molecules of quartz form the combustion chamber fly in the chamber as animpurity. This impurity is attached to steam particles and is suppliedtogether with the steam into the process tube. In this manner, a largenumber of poor semiconductor wafers are manufactured by the conventionalhorizontal oxidation apparatus.

Furthermore, a heat source must be located at the side of the distal endof the hydrogen gas guide tube longitudinally inserted in the combustionchamber. As a result, the arrangement of the apparatus is complicated tomanufacture. In addition, the manufacturing cost is increased. In theabove mentioned embodiment, a chamber of a horizontal type wasdescribed, but, it is a matter of course that a vertical type chambercan also be used. Further, a process tube of a horizontal type orvertical type can be used. In this case, any mixing means for steamgenerating gas can be used.

A condenser lens is sometimes used as a heat source located at thedistal end side of the hydrogen gas guide tube. In this case, however,the combustion position of the hydrogen gas is fixed. For this reason,the combustion position cannot be arbitrarily selected. That is,according to the type of process (especially the type of degree ofoxidation), amounts of hydrogen and oxygen gases are varied by anexternal flow rate controller. In this case, however, the sizes of theflames are different. Therefore, in order to prevent devitrification,the combustion position of the hydrogen gas must be arbitrarilyselected. However, this selection is very difficult for the conventionalapparatus.

The above embodiment of the present invention does not have a heatsource in combustion chamber 50. That is, combustion in chamber 50 canbe executed by only heating a gas before it is guided in chamber 50.Therefore, the structure of the apparatus can be simplified. Inaddition, the manufacturing cost of the apparatus can be reduced.Furthermore, a heat source need not be located at a discharge end sideof the gas guide tube. For this reason, the position of the dischargeend of the gas guide tube can be arbitrarily selected.

Another embodiment of the present invention will now be described below.

FIG. 7 shows another embodiment which uses the external combustionsystem. In this embodiment, cylindrical combustion chamber 50 is locatedabove process tube 11. Hydrogen and oxygen gases are supplied from anupper end of process tube 11. Supply tube 60 at a lower end of externalcombustion unit 10 is connected to gas inlet port 12 of process tube 11through a ball joint in which quartz tubes slide with each other. Theother parts of the arrangement are the same as those of the aboveembodiment.

Note that the distance between unit 10 and process tube 11 can bereduced because the ball joint is used. As a result, moisturecondensation as described above can be prevented without a tape heateror the like. When the distance between unit 10 and process tube 11 isreduced, the heat influence of unit 10 must be considered. In this case,however, process tube 11 may be connected to unit 10 by a ball jointwith a distance by which tube 11 is not adversely affected by unit 10,or a partition for interrupting a flame may be formed at the side ofsupply tube 60.

FIG. 8 shows still another embodiment in which the external combustionunit 10 is not used, but a combustion region for generating steam isformed in the process tube 11. In this embodiment, oxygen and hydrogengases are directly supplied in the process tube 11. Then, the gases areburned and combined using heater 13 for forming an oxide film, therebygenerating steam.

With this arrangement, as compared with the external combustion system,it is difficult to uniformly control the temperature at the oxide filmformation region in process tube 11. However, when a heating means forgeneration steam is located around process tube 11 independently ofheater 13, the temperature of the oxide film formation region can beeasily made uniform. In addition, the height of the vertical oxidationapparatus can be advantageously reduced.

When steam or oxygen and hydrogen gases are to be supplied to thevertical oxidation apparatus, the steam or the like is preferablysupplied from an upper end of process tube 11. The reason for this is asfollows. That is, a lower end of process tube 11 has an opening portionfor transporting a quartz boat. For this reason, a steam supply portmust be arranged at a position other than the opening portion. As aresult, the arrangement of the apparatus is complicated. However,according to the present invention, a gas need not be supplied from theupper end. In addition, boat 14 need not be loaded from the lower end ofthe process tube 11 but may be loaded from the upper end thereof.Therefore, the steam supply position can be variously modified.

The present invention is not limited to the above embodiments but can bevariously modified without departing from the spirit and scope of theinvention.

For example, hydrogen gas guide tube 30 and oxygen gas guide tube 20need not be constituted by a coaxial double tube but may beindependently connected to combustion chamber 50. In this case, heatingmeans 40 may be located at both or one of guide tubes 20 and 30. Whenthe flow rates of oxygen and hydrogen gases are changed in accordancewith the degree of oxidation, the size of the flame in combustionchamber 50 changes. In this case, according to the present invention,the discharge positions of guide tubes 20 and 30 can be easily changedso that the flame is not brought into contact with the wall surface ofchamber 50. This arrangement can be easily realized because the heatsource need not be located at the distal end of the guide tube unlike inthe conventional apparatus.

If half heaters 41 and 42 of heating means 40 can be vertically opened,they may be opened to rapidly cool the guide tube. However, the presentinvention is not limited to this arrangement.

FIG. 9 shows still another embodiment in which an auxiliary combustionchamber is used. In this embodiment, gas burner 72 is connected tocombustion chamber 50 through auxiliary combustion chamber 71. Burner 72forms a hydrogen supply path. Central axis 72a of burner 72 coincideswith central axis 50a of chamber 50. As shown in FIG. 10A, injectionport 72b of burner 72 is formed concentrically with burner 72. Oxygensupply path 73 is formed on an outer surface of burner 72. Heater 74 isformed on an outer surface of oxygen supply path 73.

The diameter of chamber 71 is set so as to be larger than that of path73.

In this oxidation apparatus, oxygen gas 75 is supplied to oxygen supplypath 73. At the same time, hydrogen gas 76 is supplied to burner 72.Therefore, gas 76 is heated to its ignition temperature by heater 74 anddischarged from burner 72. Then, gas 76 is ignited in chamber 71. Whengas 76 is ignited to start combustion, an oxygen and hydrogen flame 77is generated to generate steam. Flame 77 reaches a central portion ofchamber 50 through chamber 71. However, base 77a of flame 77 is locatedon a central line 50a of chamber 50. For this reason, flame 77 does notreach inlet port upper wall portion 78 of chamber 50. Therefore, inletport upper wall portion 78 is not heated to a high temperature. As aresult, thermal damage to quartz forming chamber 50 or thermaldecomposition of molecules in the quartz can be prevented.

Note that as shown in FIG. 10B, a central line 72c of injection port 72bcan be inclined downwardly with respect to central axis 72a by angle θ.In this case, the distal end portion of the oxygen and hydrogen flamefacing upward is located near central line 50a of chamber 50. As aresult, upper wall surface 50b of chamber 50 can be prevented from beingheated by distal end portion 77b of the flame.

In addition, as shown in FIG. 11, central axis 72a of burner 72 may belocated below central line 50a of chamber 50 so as to be eccentrictherefrom. In this case, distal end portion 77b of flame 77 is set so asnot to approach upper wall surface 50b of chamber 50.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

What is claimed is:
 1. An oxidation apparatus, comprising:a process tube adapted to contain a boat in which a plurality of objects to be processed are placed at predetermined intervals; first heating means for heating an interior of said process tube; a combustion chamber, located outside of and connected to said process tube via a connecting tube, for generating steam by combustion of a mixture of oxygen and hydrogen gases therein and supplying the steam to said process tube; a double-tube type structure connected to said combustion chamber, said double-tube type structure having outer and inner guide tubes for individually introducing the oxygen gas through said outer guide tube and the hydrogen gas through said inner guide tube into said combustion chamber; an auxiliary combustion chamber formed as an outlet portion of said outer guide tube; an injection nozzle formed as an outlet portion of said inner guide tube and located near a front end portion of said auxiliary combustion chamber; and second heating means provided around said outer guide tube for heating the gases to a temperature at which ignition of the gases occurs when the gases come into contact with each other; wherein said auxiliary combustion chamber comprises an enlargement portion of said outer guide tube sufficient in size to prevent a flame generated by combustion of the gases from reaching a surface of said auxiliary combustion chamber.
 2. An apparatus according to claim 1, wherein a central line of said inner guide tube coincides with that of said combustion chamber.
 3. An apparatus according to claim 2, wherein said injection nozzle is oriented at an angle sufficient to keep said flame from contacting a surface of said auxiliary combustion chamber or said combustion chamber.
 4. An apparatus according to claim 1, wherein said inner guide tube is connected in a substantially horizontal manner to said combustion chamber.
 5. An apparatus according to claim 4, wherein a central axis of said inner guide tube coincides with a central line of said combustion chamber.
 6. An apparatus according to claim 5, wherein said injection nozzle is oriented at a downward angle sufficient to keep said flame from contacting a surface of one of said auxiliary combustion chamber and said combustion chamber.
 7. An apparatus according to claim 4, wherein a central line of said inner guide tube is sufficiently lower than that of a combustion chamber to prevent said flame from reaching a surface of said combustion chamber.
 8. An apparatus according to claim 1, which comprises a third heating means provided around said auxiliary combustion chamber.
 9. An apparatus according to claim 8, wherein said third heating means is integrated with said second heating means.
 10. An oxidation apparatus, which comprises:a process tube adapted to contain a boat in which a plurality of objects to be processed are placed at predetermined intervals; first heating means, for heating an interior of said process tube; a combustion chamber, located outside of and connected to said process tube with a connecting tube, for generating steam by combustion of a mixture of oxygen and hydrogen gases therein and supplying the steam to said process tube; a double-tube type structure connected to said combustion chamber, said double-tube type structure having outer and inner guide tubes for individually introducing the oxygen gas through said outer guide tube and the hydrogen gas through said inner guide tube into said combustion chamber; an auxiliary combustion chamber formed as an outlet portion of said outer guide tube; an injection nozzle formed as an outlet portion of said inner guide tube and located near a base of said auxiliary combustion chamber; and second heating means, provided around said outer guide tube and auxiliary combustion chamber, for heating the gases to a temperature at which ignition of the gases occurs when said gases come into contact with each other wherein said auxiliary combustion chamber comprises an enlargement of said outer guide tube sufficient in size to prevent a flame generated by combustion of the gases from reaching a surface of said auxiliary combustion chamber.
 11. An apparatus according to claim 10, wherein a central line of said inner guide tube coincides with that of said combustion chamber.
 12. An apparatus according to claim 11, wherein said injection nozzle is oriented at an angle sufficient to keep said flame from contacting a surface of one of said auxiliary combustion chamber and said combustion chamber.
 13. An apparatus according to claim 10, wherein said inner guide tube is connected in a substantially horizontal manner to said combustion chamber.
 14. An apparatus according to claim 13, wherein a central axis of said inner guide tube coincides with a central line of said combustion chamber.
 15. An apparatus according to claim 14, wherein said injection nozzle is oriented at a downward angle sufficient to keep said flame from contacting a surface of one of said auxiliary combustion chamber and said combustion chamber.
 16. An apparatus according to claim 13, wherein a central line of said inner guide tube is sufficiently lower than that of combustion chamber to prevent said flame from reaching a surface of said combustion chamber. 